1. Field of the Invention
The present invention relates to a display device and a planar light source device, and more particularly to a technique which is effectively applicable to a planar light source device which radiates light propagated through a light guide plate and a display device which uses the planar light source device.
2. Description of the Related Arts
Conventionally, as a display of a mobile phone or a notebook-type PC (Personal Computer) or the like, a liquid crystal display device (a liquid crystal display unit) having a liquid crystal display panel is used.
The liquid crystal display device is roughly classified into a transmissive-type liquid crystal display device which displays an image (a video) by arranging a backlight (a light source) behind the liquid crystal display panel and radiating light from the light source to the liquid crystal display panel and allowing the light to pass through the liquid crystal display panel, and a reflective-type liquid crystal display device which displays an image (a video) by reflecting light from outside a display device on a liquid crystal display panel.
Further, the backlight of the transmissive-type liquid crystal display device is roughly classified into, for example, a direct-type backlight which arranges a light source such as a fluorescent tube in a region which is overlapped to a display region of a liquid crystal display panel, and an edge-light-type (also referred to as a side-light-type) backlight which arranges a light guide plate in a region which is overlapped to a display region of a liquid crystal display panel and arranges a light source on an end portion of the light guide plate.
The edge-light-type backlight is a backlight which radiates light to the liquid crystal display panel by propagating light from the light source which is arranged on the end portion of the light guide plate in the inside of the light guide plate, directing the light in the direction toward the liquid crystal display panel by a reflective portion formed on a back surface of the light guide plate and by diffusing the light using a diffusion plate. The edge-light-type backlight can reduce a thickness thereof compared to a thickness of the direct-type backlight. Accordingly, the liquid crystal display device having the edge-light-type backlight has been often used in a display of a mobile phone or a notebook-type PC.
Further, with respect to the edge-light-type backlight, to uniformly radiate light to the display region of the liquid crystal display panel, there has been known a backlight which uses a combination of a light guide plate to which a shape which efficiently reflects the propagating light (for example, grooves) is applied and a reflective sheet (for example, see Japanese Patent Laid-open No. 11599/2005 (patent document 1)).
Further, with respect to the edge-light-type backlight, to achieve the reduction of thickness of the backlight, for example, there has been known a backlight which is constituted of a light guide body layer (a light guide plate), a reflection layer (a reflective portion) and a diffusion layer (a diffusion plate) as the integral structure, wherein each layer is formed of a thin film sheet (for example, see Japanese Patent Laid-open Hei08-152526 (patent document 2)).